Regeneration of a fischer-tropsch reduced iron catalyst



Dec. 1, 1953 .w. c. LANNING REGENERATION OF A FISCHER-TROPSCH REDUCED IRON CATALYST Filed Deo. 15, 1948 4latentecl Dec. l, 1953 REGENERATION F A FISCHER-TROPSCH REDUCED KRON CATALYST William C. Lanning, Bartlesville, Okla., assigner to Phillips Petroleum Company, a corporation of Delaware Application December 13, 1948, Serial No. 64,958

3 Claims.

This invention relates to the synthesis of hydrocarbons and oxygen-containing materials from carbon monoxide and hydrogen, in the presence of a catalyst. In one aspect this invention relates to the regeneration of a catalyst at least partially spent in a catalytic p-rocess for the synthesis of hydrocarbons and oxygen-containing compounds, from carbon monoxide and hydrogen.

In a process of the Fischer-Tropsch type, carbon monoxide is hydrogenated in the presence of a catalyst to form hydrocarbons and oxygenatescompounds. In this type of process, operation with a uidized catalyst is most preferably employed. When so operating, feed gas comprising hydrogen and carbon monoxide is passed into the bottom of an elongated vertical reactor, and upwardly through a mass of nely divided catalytic material maintained at the desired synthesis reaction temperature. The velocity of the iniiuent gas maintains the catalytic material in a fluidized condition with the effluent gas being relatively catalyst-free.

During the course of the synthesis reaction, carbonaceous material comprising heavy waxlike product and/or carbon, accumulates on the catalyst surface until it impairs the activity of the catalyst to such an extent that removal of the carbonaceous matter is necessary. Unless the carbonaceous matter deposited on the catalyst is removed, a point is reached at which the catalyst is no longer useful, and generally must be discarded. Such practice is uneconomical in view of the fact that new catalyst must constantly be provided to replace the inactive catalyst withdrawn from the process.

In accordance with practice known to the art, when carbonaceous matter is accumulated on the catalyst to impair its activity, in a process of the type being discussed, it is treated in a regeneration step conducted either in situ, or in a separate regeneration vessel. In the latter instance, it is common practice to continuously withdraw a catalyst side stream from the synthesis chamber and to pass the withdrawn catalyst to a separate regeneration zone, regenerating the catalyst therein and returning activated catalyst thus formed to the synthesis chamber. By such practice the activity of the catalyst in the synthesis chamber is maintained at a constant level and the synthesis progresses wthout interruption.

This invention is concerned with a new and novel method for regenerating iron catalysts, which become at least partially spent during the catalytic synthesis of hydrocarbons and oxygencontaining compounds from carbon monoxide and hydrogen. When using the term at least partially spen it is meant herein, catalyst on which is deposited carbonaceous matter to a degrec that the catalyst is less active as a result of the presence of the carbonaceous material, or is completely inactive as a result thereof. A catalyst, at least partially spent, may, therefore, be one having only slightly decreased activity or it may be a completely inactive catalyst; or it may have an activity within the range of those two extremes, depending upon the extent of deposition ci carbonaceous materials on its surface.

An object of this invention is to provide a continuous catalytic process for the synthesis of hydrccarbons and oxygenated compounds from carbon monoxide and hydrogen.

Another object is to provide for the regeneration of a iiuidized iron catalyst employed in the catalytic synthesis of hydrocarbons and oxygenated compounds from carbon monoxide and hydrogen.

Another object is to provide a process for the catalytic hydrogenation of carbon monoxide wherein hydrocarbons and oxygenated compounds are produced in the presence of a catalyst having a constant activity level, maintained by continuously withdrawing a portion of catalyst, at least partially spent, from the synthesis zone, regenerating the withdrawn catalyst and returning iron catalyst thus activated to the Synthesis.

Other objects will be apparent, to those skilled in the art, from the accompanying discussion and disclosure.

In accordance with a preferred embodiment of this invention, hydrocarbons and oxygen-containing compounds are synthesized from carbon monoxide and hydrogen in the presence of a fiuidized iron catalyst, in a process wherein catalyst, at least partially spent, in the synthesis zone as the result of deposition thereon of carbonaceous product materials, is withdrawn from the synthesis zone and passed to a separate regeneration zone, reactivated therein and returned to the synthesis. Fluidized iron synthesis catalyst laden with carbonaceous material and Withdrawn from the synthesis zone is introduced at a controlled rate into a regeneration chamber, or furnace, through a feeder which drops the catalyst material on slots for uniform distribution in an upper portion of the regeneration chamber. In this chamber it is contacted in countercurrent iiow, at a rate not exceeding substantially free settling conditions, with excess oxygen, or a suitable oxygen-containing gas, at a temperature at which the carbonaceous deposits on the surface of the catalyst are oxidized to gaseous oxides, and at which concomitantly formed iron oxide is fused. Droplets of molten iron oxide are passed on downwardly through a portion of the regeneration zone below the upper portion already discussed, under substantially free settling conditions, in fceuntercurrent flow "and heat vexchange relation with .oxygen introduced below, at a temperature lower than the fusion temperature of iron oxide, causing the iron oxide droplets t solidify. The solid iron loxide particles thus formed are removed from the regeneration zone, and reduced by hydrogen to .form :reactivated fluidized iron catalyst, of rthe original particle size, which is then recycled to the synthesis zone.

In another embodiment I may utilize an oxygen-containing gas, often air, and conduct the combustion in the regeneration zone without fusing the concomitantly formed iron oxide. rlhis embodiment, i. e., operating vwithout Yfusing the iron oxide, is .less preferable than that lalready discussed, :although it provides for removal of the carbonaceous matter from the catalyst surface without requiring rigid control of process conditions, i.-e.., ferric loxide or ferrosic .oxide is formed over a broad temperature range and is ,easily reduced.

In order to more clearly illustrate my invention, reference is made to the following description 4and to the figure, in which one method oi operating my .process will be specifically disclosed. The .figure is a flow-diagram which diagrammatica-lly illustrates one formof apparatus in which my process may be practiced. to be understood that the flow diagram is diagrammaticionly andA may be altered in manyrespects by those `skilled in the art and yet remain within lthe ,intended scope of my invention.

VReferring then to the figure, hydrogen from line I0 and carbon monoxide from line yII are admixed .in line I2 in a hydrogen to `carbon monoxide mole ratio within the range of 1.7:1 to 2.3:'1, preferablyiabout 2:1, and the resulting admixture -is introduced into the lower portion of synthesis zone i3 Which-contains a promoted iron catalyst having a mesh size within the limits yof 80 to 400 mesh, at aspace velocity within the limits of 1500 to 3500 standard gas volumes per catalyst volume per hour. Under such conditions of catalyst particle size and space velocity, the catalyst in zone E3 ismaintained in a iiuidized, dense-phase suspension. Synthesis zone I3 is maintained at a temperature within the limitsof 560 to 620 F. and -at a pressure within the range of 5 .to 30 atmospheres. Total -eiiluent from zone -|3 is passed through line I 5 `to product separation vrneans I'I' comprising coolers, separators, distillation equipment, storage tanks and the like, not individually illustrated, which can be used to effect a separation of various selected product fractions introduced from line It. The total product in line I6 contains Aa large amount of hydrocarbons along .with a smaller amount of oxygenated compounds .and a large amount of Water. Tail ygas comprisinghydrogen,carbon monoxide and carbon dioxide is Withdrawn from zone II through line I8 and .recycled to synthesis zone I3 through lines I9, 2| .and |.2,.or withdrawn ngpart or in whole, as desired, through line 22. The preferred vmole ratio .of recycled tail gas to fresh gas charge is usually within the range .of 2:1 to 5:1. A normally gaseous hydrocarbon stream is withdrawnfrom zone |71 through line 23. A gasoline stream is Withdrawn from zone It isA I'I through line 24 and a heavier hydrocarbon stream, i. e., product boiling above approximately 400 F., is withdrawn through line 26. Wax and other heavy materials are Withdrawn from zone I'I through line 2l. Water is withdrawn through line 28.

During the operation of the synthesis step in zone I3, `high molecular V-weight wax and waxlike products and/or carbon accumulates on the catalyst surface and after a period of time such an accumulation is so great as to impair iluidization of the Acatalyst and to cause the catalyst lactivity to -decrease to an undesirably low level. .In `order` to maintain a desired level of catalyst activity and aconstant state of catalyst uidization in synthesis zone I3, a continuous catalyst side stream may be passed from zone I3 through llines Ill and 2a vte 'hopper 3| containing catalyst at least partially spent in zone I3 to be regenerated in regeneration zone 33. Catalyst withdrawn from zone I3 in this manner often carries with it small quantities of valuable relatively volatile material that may be recovered ahead of the regeneration in zone 33. This may -be done by iiushing the catalyst zody in zone 3| with `an .inert ushing gas such .as steam, flue gas or the like, introduced into hopper 3| through line 25. Flushing gas .containing relatively volatile product may then be removed from zone 3| through line 2G. Partially spent .catalyst from hopper 3i is passed ata controlled rate by means .of sta-r wheel feeder 32 into regeneration zone 33. Catalyst material iroizrfeeder-SZ lis dropped on to perforate distributor plate 36. By -means of distributor plate .35 and star valve .32 the rate of .new of catalyst material .through regenera- .tionzone fis controlled so that flow of catalyst particles is within Athe range of substantially free settling conditions. Catalyst materials ow uniformly kdownwardly .from lplate 3S in countercurrent flow relation .through combustion section A positioned in an upper portion of regeneration zone 33, with oxygen, at a temperature at which carbonaceous matter on the catalyst surface is converted togaseous oxides, and iron oxide con- Vcoinitantly formed is fused. Gaseous oxides thus formed are withdrawn from regeneration zone 33 through 'line A3l? .and passed to gas separator 3E, wherein any entrained solid iron oxide materials are separated from the gas. Solid iron oxide particles separated in zone 38, are passed through lines 39 Yand 29 to hopper -3| and then returned to zone 33. vGas from zone 38 is passed through line 4| to carbon dioxide removal system #l2 comprising various absorption steps, known to those skilled in the art, suitable for removing carbon dioxide from zone 38 eiiluent. Zone d2 may comprise an ethanolamine .absorp- 'ion system, 4well known to those skilled in the art, wherein carbon dioxide is absorbed in ethanolamine and subsequently removed in a separate stripping zone. In such an instance, unreacted oxygen present in the gas entering zone i2 remains unabsorbed and .is recovered substantially free of carbon dioxide. Carbon dioxide from zone '42 may -be withdrawn through lines 3 and 'Lili to further utilization, .not shown. However, if desired, carbon 'dioxide from 'line d'3 may .be recycled through Alines .4.6, ,2| and I2 to synthesis zone I3. Carbon dioxide-freegasfrom zone d2, comprises unreacted oxygen in .a .major proportion, together with small .amounts of nitrogen and carbon monoxide, and is Withdrawn from .zone i2 through line il, and ,passed Vin Whole or in part, as desired, through line 48 to oxygen purification means, not shown. Preferably, however, all or at least a part of gaseous material from line 4i is passedthrough line i9 and admixed in line 52 With fresh oxygen or a fresh oxygen-containing gas from line 5l. The resulting oxygen-containing admixture in line E2 comprises preferably from 50 to 90 per cent or more of oxygen, and is introduced through line 53 into cooling section B of regeneration zone 33, subjacent combustion section A, already described, at a temperature usually from about to 700 C. The temperature of the oxygencontaining gas thus introduced into zone 33 is below that at which iron oxide, concomitantly formed in combustion section A of zone 33, exists in the molten state. Oxygen-containing gas, introduced from line 53 into cooling section B of Zone 33, passes upwardly therein in countercurrent flow and in heat exchange relation with molten iron oxide flowing Adownwardly at a rate not exceeding substantially free settling conditions. Cperating in this manner, the molten iron oxide droplets are cooled by the oxygencontaining gas rising through cooling section B, and solid iron oxide particles of a size equivalent to the original iron catalyst particles are formed, and collect in the bottom of zone t3. Iron oxide particles thus formed accumulate in the bottom of Zone 33, forming a gas seal therefor, and are withdrawn at a controlled rate through star Wheel feeder valve 5d and passed through line 55 to an iron oxide reduction step. In some instances, depending upon whether or not free settling conditions of the liquid oxide droplets are generally exceeded, or are so closely approached that some individual particles exceed such rates, a limited amount of agglomeration may take place. In such cases, it may be desirable to grind the iron oxide material in line 5t to the desired mesh size for ultimate use in Zone i3, although generally, agglomeration does not take place, and grinding is not required. When it is necessary to regrind the iron oxide particles, material from line 56 is passed through line 5l to grinding means 58. Iron oxide of the desired mesh size is withdrawn from grinding Zone at through line 553 and passed through line El to iron oxide reduction zone S2. However, in most instances grinding is unnecessary and under those conditions, iron oxide from line de is passed around grinding zone 58 through lines 63 and iii to reduction zone 62. In Zone 62, iron oxide is reduced to iron with hydrogen introduced from lines 63 and t4, admixed when desired with recycled hydrogen from line l0, described hereafter, at a temperature usually within the range of about 315 to 485 C. Iron oxide reduction prod ct from zone 62 comprises appreciable amounts of iron and some iron oxide. Off gas from iron oxide reduction zone $2 comprises primarily hydrogen and steam, which may be withdrawn through line el and passed through lines t@ and @t to water removal zone l5, usually a cooling step wherein Water condensate is formed, and removed from recycled gas introduced from line tit. Water-free recycled hydrogen gas is then passed from zone 'l5 through lines l@ and @Il to zone 62. However, if desired, all or a portion of the gas in line 'lil may be passed to synthesis Zone E3 through lines t3, d6, 2i and l2. Oi gas in line 69 may be withdrawn through line 'H when desired to further utilization, not shown. Water may be Withdrawn from zone 'l5 through line 65. Fluid activated iron catalyst suitable for utilization in synthesis zone I3 is withdrawn from iron oxide reduction zone 62 through line 12 and recycled to synthesis zone I3 through line i2 in admixture with fresh feed and recycled tail gas, introduced as already described.

When initiating operation in zone 33, combustion zone A may be brought to temperature by iirst burning a gas combustion mixture therein, introduced through line d6, comprising fuel gas from line 45 and oxygen, or an oxygen-containing gas, from lines 52 and 50. Subsequent to developing the desired temperature in combustion section A of zone 33, the flow of the gas combustion mixture through line @il may. be terminated or lessened, and the temperature therein at least partly sustained by the burning of carbonaceous matter in the presence of oxygen, already discussed. Temperatures in the combustion section are often as high as from 150G-1600 C., usually within the range from 14:00-1700o C.

The minimum amount of oxygen introduced into zone 33 through line 53 is that quantity sufficient to burn all carbonaceous matter deposited on the catalyst surface, and to oxidize all iron to iron oxide, the latter oxidation taking place concomitantly. However, the total amount of oxygen introduced through line tt is generally from 5 to 15 per cent above the minimum amount discussed above, to insure complete oxidation of oarbonaceous matter and iron catalyst at all times.

When air is employed as the oxygen-containing gas in the practice of my invention, some ferric oxide may be formed along with magnetic iron oxide, whereas when oxygen or an oxygenrich gas is employed and the oxide is fused, magnetic iron oxide is formed. The magnetic iron oxide, upon reduction, provides an activated iron catalyst having an activity higher than that of the ferric oxide reduction process.

For convenience and clarity certain apparatus such as pumps, surge tanks, accumulatore, valves etc. have not been shown in the drawing. Obviously such modifications of the present invention may be practiced Without departing from the scope of the invention.

Any iiuid iron catalyst employed in the synthesis of hydrocarbons and oxygenated compounds by the catalytic hydrogenation of carbon monoxide, when at least partially spent during the synthesis as a result of carbonaceous deposits accumulated therecn, may be regenerated in accordance with my invention. Although iron alone may be used as a catalyst in the synthesis of hydrocarbons and oxygenated compounds from carbon monoxide and hydrogen, promoted iron catalysts are generally employed. Such promoters may be, for example, alkali metals or alkaline earth metals or their oxides, thoria, or various other materials. Among the promoters more generally utilized are potassium oxide, calcium oxide, and aluminum oxide. Very slight loss of promoter, if any at all, occurs when regenerating iiuidized promoted iron catalyst in accordance with my invention.

As will be evident to those skilled in the art various modiications can be made or followed in the light of the foregoing disclosure and discussion, Without departing from the spirit or scope of the disclosure or from the scope of the claims.

I claim:

1. In the regeneration of a particulate iron catalyst containing a metal oxide promoter and having a mesh size within the limits of and 40u employed inztherconyersion oi carbon .monoxide and hydrogen to .hydrocarbons and oxygen-containing compounds and at least partially spent by deposition thereon of 4carbonexzeous matter during said conversion, wherein said 'spent catalyst `is .freed of carbonaceous matter rby yoxidation and said iron is concomitantly oxidized, 'and wherein magnetic iron 'oxide thus formed is sub-- sequen-tly'reduced'to metallic iron, 'the improve :nent in freeing said catalyst Vof carbonaceous matter deposited thereon comprising introducing such spent catalyst into an upper section of a regeneration zone of suiicient length to permit oxidation of carbonaceous matter and :of iron, fusion of viron oxide, and solidication of iron oxide ias herein subsequently fset forth and thereN in contacting saine at a :temperature the limits of 14004700" C. in vcountercurrent flow .relation under free settling conditions with an up wardly vflowing gas containing at least 80% oxygen introduced tlirougha section Aof said regeneration zone subjacent said upper section where-- by carbonaceous matter on the Acatalyst `surface is burned to form 'gaseous oxides and the ,iron is 'completely converted to magnetic iron oxide and whereby magnetic iron .oxide concomitanztly formed is fused to form unagglomerated liquid droplets, withdrawing combustion gas'frorn said regeneration zone, and passing droplets of fused magnetic iron oxide downwardly through said subjacent section under free settling conditions in vcountercurrent flow and in heat exchange relation with said gas containing oxygen introduced into said subjacent section at a temperature oi' 50-700 C. and to be contacted with catalyst in said upper section, whereby said droplets are cooled and form unagglomerated solid magnetic iron oxide particles.

2. The method of removing carbonaceous matter deposited on the `surface of a nuidizable iron catalyst which has become spent inthe synthesis of hydrocarbons from carbon monoxide and hydrogen, which method comprises 'contacting said catalyst, in a regeneration zone, in countercurrent i'iow relation under free settling con-di tions, with upwardly owing oxygen in suiiicient amount and at a temperature suiiiciently high to support combustion of said vcarbonaceous matter and to oxidize the iron substantially completely, whereby magnetic iron oxide is Acontornitantly `formed and whereby said oxide is fused to orrn unagglomerated liquid droplets, passing molten iron 'oxide thus formed downwardly in said zone in countercurrent now and heat exchange `relation with oxygen at a .temperature lower than the solidication temperature of said oxide to cool same and form solid magnetic iron oxide particles free of :said carbonaceous matter,

Ei said regeneration ."zone being yof sufficient length to permit combusti-on of carbonaoeous matter, oxidation of iron, and solidi-cation yas aforesaid, and recovering Vsaid Asolid magnetic iron oxide particles.

3. In the regeneration of a iuidzable iron catalyst employed `in the Vconversion of 'carbon monoxide and hydrogen to hydrocarbons and oxygen-nontaining compounds and at least partially spent by deposition thereon of carbonaceous matter during said conversion, said catalyst having a ,particle size not greater than 30 mesh, 'wherein*su'chspent-catalystis freed of carconaceous matter lby oxidation and the iron is oxidized and 1wherein magnetic iron oxide thus formed is subsequently reduced to metallic iron, .the improvement which comprises introducingr such spent catalyst into an upper part of fa regeneration .zone vof suicient length to permit oxidation of :earbonaceous matter and iron, fusion of oxide, and solidiication or oxide as subsequently set forth, :countercurrently contacting lsaid catalyst, in said zone, under free settling conditions, with an upwardly owing gas containing at least 50 per cent oxygen introduced into a lower part of said zone in sufficient amount to remove said carbonaceous matter and completely oxidize lsaid iron, whereby magnetic iron oxide is concomitan-tly ,formed and whereby said magnetic -oXi-de is fused to form unagglomerated liquid droplets, and passing said fused magnetic oxide downwardly under free Ysettling conditions through said lower part of said zone countercurrently to said gas, which is introduced into said lower part at a tempera-ture lower than the solidi-cation temperature of said magnetic oxide, whereby said magnetic oxide is lcooled `to form solid fluidizable magnetic iron oxide particles, and recovering sm'd solid iron oxide.

WILLIAM C. LANHNG.

References Cited :in the ile of this patent UNITED STATES PATENTS Number Name Date 2,015,053 Freeman Sept. 17, 193 2,030,627 Freeman Feb. 11, 1935 2,038,251 rVogt Apr. 21, 1936 2,040,682 Bacon .et al May 12, 1936 2,365,720 Neighbors Dec. 26, 1944 2,420,049 Martin May 6, 1947 V2,438,584 Stewart Mar. 30, 1948 2,455,419 Johnson Dec. 7, 1948 2,467,803 Herbst Apr. `9, -1949 2,477,454 'Heath July 26, 1949 v2,483,850 4,Segura Oct. 4, 1949 2,488,150 `Wa1den `et al Nov. 15, 1949 

2. THE METHOD OF REMOVING CARBONACEOUS MATTER DEPOSITED ON THE SURFACE OF A FLUIDIZABLE IRON CATALYST WHICH HAS BECOME SPENT IN THE SYNTHESIS OF HYDROCABONS FROM CARBON MONOXIDE AND HYDROGEN, WHICH METHOD COMPRISES CONTACTING SAID CATALYST, IN A REGENERATION ZONE, IN COUNTERCURRENT FLOW RELATION UNDER FREE SETTLING CONDITIONS, WITH UPWARDLY FLOWING OXYGEN IN SUFFICIENT AMOUNT AND AT A TEMPERATURE SUFFICIENTLY HIGH TO SUPPORT COMBUSTION OF SAID CARBONACEOUS MATTER AND TO OXIDIZE THE IRON SUBSTANTIALLY COMPLETELY, WHEREBY MAGNETIC IRON OXIDE IS CONCOMITANTLY FORMED AND WHEREBY SAID OXIDE IS FUSED TO FORM UNAGGLOMERATED LIQUID DROPLETS, PASSING MOLTEN IRON OXIDE THUS FORMED DOWNWARDLY IN SAID ZONE IN COUNTERCURRENT FLOW AND HEAT EXCHANGE RELATION WITH OXYGEN AT A TEMPERATURE LOWER THAN THE SOLIDIFICATION TEMPERATURE OF SAID OXIDE TO COOL SAME AND FORM SOLID MAGNETIC IRON 